This issue could be caused by either a slow Internet connection or large e-mail attachments. As such you should:
- You should switch your e-mail client to IMAP for incoming e-mails – this will give you the option to skip attachments when downloading e-mails and simply retrieve the message as opposed to POP3 with which the whole e-mail message (along with the attachment) is automatically downloaded. This should resolve the issue if it was indeed caused by a large attachment.
- Check your Internet connection speed and make sure that there are no other ongoing downloads at that time. If the issue persists, kindly contact your ISP.